With the progress of medical science and technical art, living quality of modern people is improved day by day. For example, sleeping quality of a patient with obstructive sleep apnea syndrome (OSAS) can be improved by using a positive airway pressure breathing apparatus. The positive airway pressure breathing apparatus needs a fan motor to provide air to a user, so the fan motor is one of key members of the positive airway pressure breathing apparatus.
FIG. 1 is a three dimensional cross sectional view of a conventional brushless fan motor of a positive airway pressure breathing apparatus, and FIG. 2 is a three dimensional exploded view of FIG. 1. Referring to FIGS. 1 and 2, a brushless fan motor 1 is disclosed in U.S. Pat. No. 6,960,854. The brushless fan motor 1 includes an upper case 2 and a lower case 3 combined with the upper case 2. A bearing 13 is disposed in the lower case 3, and a bearing 14 is disposed in the upper case 2. A rotating shaft 4 is disposed through the bearings 13 and 14. A fan blade turntable 7 is fixed at the rotating shaft 4 to be rotated with the rotating shaft 4. A toric magnet 5 is fixed at the rotating shaft 4, and the toric magnet 5 is surrounded by a toric coil 6.
When a current is applied to the toric coil 6, an induced electromagnetic field is generated to rotate the toric magnet 5, and the fan blade turntable 7 is thereby rotated with the toric magnet 5. An air flow is generated when the fan blade turntable 7 is rotated. The air can be output from an outlet 25 to a user through a pipe (not shown) connected with the outlet 25.
However, in the conventional technique, the bearings 13 and 14 are respectively disposed at the lower case 3 and the upper case 2. Due to assembling tolerance between the upper case 2 and the lower case 3, the bearings 13 and 14 may not be positioned in the same central axis. This results in an eccentric rotation when the rotating shaft 4 is rotated, and therefore, huge noise is generated when the positive airway pressure breathing apparatus is worked.